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Location of footing reinforcement

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Longitudinal reinforcing in a footing is simply tie bars --- something to tie 
the transverse horizontal reinforcing and wall reinforcing to.

*If* the longitudinal reinforcing was intended to resist moment, the minimum 
reinforcing would have to conform to that required for flexural members.  
Does it?

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Richard Lewis asked:

. > Let me ask an engineering judgement question which I hope sparks a lot of
. > controversy and causes many different opinions to be brought forth.
. > 
. > A week or so back someone had posted a question regarding minimum 
. > thickness of a concrete footing. It reminded my of a engineering 
. > philosophy question of where to locate the longitudinal reinforcing in a 
. > continuous strip footing. I think traditionally we locate longitudinal 
. > reinforcing in a strip footing at the bottom. My question is WHY?  What 
. > is the purpose of longitudinal reinforcing?  Is it to:
. >   -span across local settlement of the soil?
. >   -tie the wall footing together to prevent 
. >      it from pulling apart, somewhat similar
. >      to a bond beam at the top of a wall?
. >   -somehow provide strength to the footing element?
. > 
. > Why does it have to be at the bottom to provide these functions?  
. > Wouldn't it make more sense to put it at the top?  For strength, a larger 
. > load can be supported over a slight settlement using negative moment at 
. > ends then a positive moment at the middle. It would be easier to place 
. > the reinforcing and not worry about bottom cover if the contractor were 
. > able to pour the concrete to say 2 inches from the top of footing, lay the
. > reinforcing in place and then pour the rest of the concrete. What 
. > difference does it make if the reinforcing is top or bottom in regards to 
. > shrinkage?
. > 
. > I look forward to reading many different opinions on this topic.
. > 
. > 
. > __________________________________________________
. > 
. > Richard Lewis, P.E.
. > Missionary TECH Team
. > rlewis(--nospam--at)techteam.org
. > 
. > The service mission like-minded Christian organizations
. > may turn to for technical assistance and know-how.
. >